<!DOCTYPE html>
<html>
<head>
	<meta charset="UTF-8">
	<title>Document</title>
	<style>
		input[placeholder], [placeholder], *[placeholder], ::-webkit-input-placeholder { 
			color:red !important; 
		} 
	</style>
</head>
<body>
	
	<input type="text" placeholder="测试一下">

</body>
</html>